The present invention relates to a new and improved apparatus for the determination of the thermal efficiency of a chemical reaction. In the context of this disclosure the term "thermal efficiency", or equivalent expressions, generally refer to the quantity of heat consumed or liberated in a chemical reaction.
When carrying out chemical reactions on a large scale basis as accurate as possible knowledge of their kinetic behavior is necessary. Since practically every chemical reaction is associated with a more or less large conversion of energy and the transformed quantity of heat is in a certain relationship to the reaction rate and the concentration of the reaction product it has been found that thermal analysis constitutes a practical and good expedient for obtaining information concerning the reaction kinetics of the most different reactions.
The invention of this development concerns an apparatus, generally designated as a thermal flow calorimeter, for determining the thermal efficiency of a chemical reaction, and which apparatus is of the type incorporating a reaction vessel equipped with a stirrer mechanism, a heat exchanger for influencing the temperature of the reaction mixture, the heat exchanger being located in the circulation system of a heat transfer fluid medium e.g. heat transfer liquid. Further, there are provided means for circulating the heat transfer fluid medium, measurement feelers for the temperature of the reaction mixture and the heat transfer fluid medium, and a regulation system cooperating with the measurement feelers for controlling the temperature of the reaction mixture. The regulation system embodies a reference value transmitter for the temperature of the reaction mixture and a temperature regulator which opposingly changes the temperature of the heat exchange fluid medium entering the heat exchanger for deviating the temperature of the reaction mixture by a multiple of the value of such reference value deviation.
A state-of-the-art heat flux calorimeter or thermal flow calorimeter of this type has been disclosed, by way of example, in Swiss Pat. No. 455,325. With this prior art calorimeter the heat exchanger is constructed as a pipe coil arranged within the reaction vessel. The pipe coil forms part of a circulation system in which there is circulated a suitable heat transfer medium. In the circulation system there is provided a cooling device which cools the medium down to a constant temperatuure throughout the entire reaction time. After the cooling device there is connected a heating device which heats the medium to the momentarily required temperature. By means of the heating device a regulator controls the temperature of the medium which flows into the pipe coil in such a manner that by means of the pipe coil there is always delivered or withdrawn, as the case may be, just so much heat from the reaction mixture and corresponding to the thermal efficiency that the temperature of the reaction mixture follows a preprogrammed time function. Under these conditions the quantity of heat which is consumed or liberated respectively, by the medium per unit of time through the agency of the pipe coil constitutes a measure for the thermal efficiency of the reaction. In order to determine this quantity of heat there is continually recorded the difference of the temperature of the heat transfer medium which prevails at the input and at the output of the pipe coil. Under the precondition that there prevails a constant rate of flow through the pipe coil this temperature is proportional to the quantity of heat which has been consumed or liberated, as the case may be, between the measurement points.
One of the drawbacks of this prior art thermal flow calorimeter resides in the presence of a pipe coil internally of the reaction vessel. Due to the arrangement of such pipe coil within the reaction vessel the elimination of the reaction residues which is required after each measurement is rendered extremely difficult. Although it might appear to be obvious to simply replace the reaction vessel which is equipped with the internally arranged pipe coil by means of a double-wall reaction vessel such is not possible by virtue of the specially employed measurement principle, since in the case of a double-wall reaction vessel completely different heat flow conditions prevail which cannot be so simply monitored, and which for such special measuring principle falsify the measurement results and thus render such less reliable for reaching conclusions regarding the thermal efficiency of the chemical reaction.
One of the most decisive drawbacks of the heretofore known thermal flow calorimeters resides in the stark dependency of the measuring accuracy upon the constant flow rate per unit of time of the quantity of heat transfer medium flowing through the pipe coil. It is particularly difficult with high throughput and especially in the case of non-isothermic reactions to maintain a constant throughflow rate since the viscosity characteristics of the heat transfer fluid medium markedly vary.
A further drawback of the prior art thermal flow calorimeter resides in the nature of the regulation system for the temperature of the heat transfer medium. This system functions in accordance with the throughflow principle and is much too sluggish for higher throughflow rates. Additionally, it is relatively uneconomical since owing to the series arranged cooling and heating devices it is necessary to initially cool the entire circulating medium to a constant temperature which is below the temperature which is just required and then such must be again heated to the required value.
The above-discussed drawbacks and limitations have resulted in the recognition that the heretofore known thermal flow calorimeter is not satisfactory in practice.